Adjustable coating pan

ABSTRACT

A new coating pan is provided which renders the regulation of the coating width very easy. The characteristic features of the coating pan are the uniform distribution of the liquid to be coated over the whole width of the pan and the provision of movable end dikes which are so designed that the liquid may flow over and under the dikes. By means of a screw type regulating device, the dams may be moved over a part of the coating width, without creating stagnant zones in the pan.

iJnite States Patent 1191 Van Regenmortel 1 Feb. 4, 1975 1 ADJUSTABLE COATING PAN 2,368,176 1/1945 Trist 118/407 75 I L d C I V 2,968,279 1/1961 Peterson 1 118/407 1 1 memo m 3,032,007 5/1962 McCauliff 118/259 x Regehmoflel, Hoboken, Belgium 3,339,485 9/1967 Rytterholm 118/259 x [73] Assignee: Agfa-Gevaert, Mortsel, Belgium R 1 F db Primary Examinerona d e] aum [22] Filed May 1973 Attorney, Agent, or Firm-William J. Daniel [21] Appl. No.: 356,440

[57] ABSTRACT [30] Foreign Application Priority Data A new coating pan is provided which renders the regu- May 3, 1972 Great Britain 20665/72 latidh Of the Coating Width very easy- The eheteetetistic features of the coating pan are the uniform distri- [52] US. Cl. 118/419, 118/429 butidn of the liquid to be coated ever the Whole width 51 1111. c1. B05c 3/12, 1305c 3/18 of the p and the provision movable end dikes [58] Field of Search 118/429, 419, 423, 407, which are so designed that the liquid my flow over 118/259 and under the dikes. By means ofa screw type regulating device, the dams may be moved over a part of the [56] Refer n Cit d coating width, without creating stagnant zones in the UNITED STATES PATENTS 2,168,997 8/1939 Lankes et a1. 118/419 14 Claims, 10 Drawing Figures PATENTED FEB 4'97?) SHEET 2 BF 4 PATENTED FEB 4I975 SHEET 3 OF 4 PATENTEDFEB 41915 3'. 863 500 SHEET u 0F 4 Fig. 6

ADJUSTABLE COATING PAN The invention relates to a coating apparatus, and more particularly to a coating apparatus for applying liquid coating composition to a travelling web. The invention is particularly, but not exclusively, concerned with apparatus used for coating substrate or emulsion layers during the manufacture of photographic film.

A preferred embodiment of the invention which will be described hereinafter consists of a coating pan intended for providing a continuous high polymer web with a subbing layer.

During the manufacture of photographic film, an aqueous solution of gelatin in which light-sensitive substances have been dispersed must be spread onto a web of a high polymer substance such as polyethylene terephthalate, polycarbonate, cellulose triacetate, etc. As said high polymer substance is essentially hydrophobic, there exists an incompatibility between the surface properties of the latter and those of the aqueous gelatin solution, caused by the essentially hydrophilic character of same. Applying said aqueous gelatin solution directly onto said high polymer web would result in a lack of quality of the finished product.

in order to overcome this inconvenience one may apply at least one subbing layer which is capable of firm adhesion both to the emulsion layer and the high polymer web. Apart from the fact that the width of a high polymer web to be used for the manufacture of photographic materials is subjected to slight variations as a consequence of the production process, the format of the ultimate sheet material plays a part too in determining a kind of optimal coating width, enabling an economical splicing and/or cutting of the finished web.

For reasons of economics, in modern high-speed coating machines, switching from one coating width to another is preferably carried out without stopping the machine. As a consequence thereof, the net coating width has to be adapted to the new situation and therefore the object of this invention is to provide a coating apparatus by which the coating width may be regulated easily and continuously.

Coating systems permitting a regulation of the coating width have already been described. They generally consist ofa coating pan provided with displaceable end dikes or dams by means of which the coating width is adjusted. They suffer however from the inconvenience that this displacement can be achieved only with difficulty during a continuous process. Moreover, the displacement of the end dams gives generally rise to the formation of idle corners causing the evaporation of a part of the solvent resulting in an accumulation of dried substance in these areas. Moreover, prior art coating pans require to be provided with auxiliary devices in order to prevent any leakage between the backing roller and the dams and between the dams and the bottom of the pan. Such leakage would result in an accumulation of solute in such places, due to evaporation of solvent. By way of example it has been proposed to provide means for pumping liquid between the end dams and the roller in opposition to the natural flow of the coating solution. In certain cases the dams ofthe known coating pans require to be accurately shaped to conform to the periphery of the backing roller and thus have to be modified when the backing roller is reground to remove defects due to wear.

The present invention aims are remedying the above mentioned drawbacks.

According to the present invention there is provided a coating apparatus for applying a liquid coating composition to a moving web, comprising a rotatable backing roller for determining a path for the web, a coating pan disposed under said backing roller for holding coating solution in said web path, and means for continuously delivering coating solution into said pan over the full length thereof, said coating pan having end dams which determine the effective internal length of the pan and which are shaped and located so that their tops conform to the curvature of the surface of the backing roller but are spaced from that surface, at least one of said dams being displaceable for varying said effective length, and said coating pan also having an overflow edge over which liquid can continuously discharge from the pan over the whole of said effective length, which overflow edge is at a level above the level of the lowest points on the tops of said dams.

Preferably at least one of said dams is provided with adjustment means, preferably screw adjustment means, which is accessible at an end of the coating pan and by which the position of the dam can be infinitely varied during operation of the apparatus.

The invention includes apparatus for applying a liquid coating composition onto a moving web, comprismg:

a. a rotatable backing roller for determining-a defined path for the web,

b. a coating pan disposed under said backing roller and provided with end dams which are displaceable according to the length of the pan, said dams being shaped to substantially conform to the curvature of the backing roller,

c. (a) liquid supply opening(s) through which coating composition may be supplied to the coating pan the composition being uniformly distributed over the maximum coating width capacity of the coating d. collecting pan(s) for collecting liquid which may flow away at either extremity of the coating pan, and

e. an overflow edge for controlling the level of the coating composition in the coating'pan between the end dams on coating, and means for collecting liquid flowing over said edge.

For obtaining a well-defined coating edge and a highly uniform application of coating composition to the web, it is desirable to shape the end dams to reduce the sizes and to increase the stabilities of the meniscusses which form at the rear ends of the dams (the ends from which the web leaves the coating pan) and along the top outer edges of the dams. Preferably the inner faces of the upper portions of the end dams slope upwardly and outwardly towards the tops of the said dams. Preferably also the outer faces of the upper portions of the end dams slope upwardly and inwardly towards the tops of the said dams.

The inherent advantages of the invention will be come apparent to those skilled in the art in the light of a preferred embodiment with reference to the accompanying figures in which:

FIG. 1 represents a top view of a high polymer web;

FIG. 2 represents a cross-section of the coating apparatus;

FIG. 3 illustrates the construction ofthe coating pan;

FIG. 4 represents the circuits for feeding and regulating the amount of coating solution;

FIGS. 5a to 52 represent details relating to liquid flow in the vicinity of an end dam;

FIG. 6 represents the end dam adjusting mechanism.

According to FIG. I a web ofa high polymer material 1 is provided bearing a subbing layer which extends over the width of the web and the extended ends of which are indicated by the dash lines 2. When another web 3 having a narrower width must be joined to the former by adequate means, the coating width will be limited by the dash lines 4 in this case. In order to do this conveniently the path of the subbing layer will pass from dash line 2 to dash line 4 by following a path indicated by dash line 5 in the immediate vicinity of the place where webs l and 3 are joined to each other.

FIG. 2 is a cross-sectional view of the coating apparatus. The liquid coating solution 10 is supplied to two distribution channels II provided with openings 16 arranged adjacent to the coating pan 12. The coating solution flows from the openings I6 into the pan 12 at a rate which is substantially uniform over the length of the pan. The top of the pan is concave and matches the curvature of the surface of-the backing roller 13 bearing a web 1. Within the coating pan there are movable end dams 14. These dams are mounted so that there is a clearance between the bottom of each dam and the bottom 25 of the coating pan in order to allow a free flow of coating solution beneath the said dams. In a preferred embodiment, the amount of solution flowing under said edges may amount to from l5 to 40 71/, and preferably to 25 70, ofthe total amount flowing through the liquid supply opening(s) 16. There is also a clearance between the tops of the end dams and the web I when the apparatus is in use.

Due to the concave shape of the coating pan it holds a quantity of coating solution up to a predetermined level. The web 1 is carried by the backing roller 13 into contact with the coating solution in the direction indi' cated by the arrow so that a layer of the coating solution is applied to the web. There is a continuous discharge of coating solution over the front overflow edge of the pan. The overflowing solution is collected in a trough l7 and fed to a replenishing station 15 through a conduit 26. In the replenishing station 15 fresh coating solution is supplied through the conduit 27 in order to compensate for the amount which is consumed. The coating solution then flows through conduit 18 to pumping and regulating devices whereupon it is again fed to the distribution channels 11. The coating station may be completed with thickness regulating devices, such as air knives, trailing blades, etc.

FIGS. 3 and 4 illustrate the flow of the coating solution in the coating pan. Through inlet openings 16 the coating solution is pumped into the channels 11 by means of a pumping device 20. I

When the maximum level in said channels is reached, the coating solution flows into the coating pan 12 over the entire length thereof. The liquid flowing into the part of the pan between end dams 14 is sufficiently restrained by these dams from flowing to the open ends of the pan, to cause the liquid level to build up in the area between these dams, up to the level of the front overflow edge of the pan. Some of the liquid flows over and beneath the dams 14 however and this liquid flows from the open ends of the pan and is received by the trough I7.

In order to illustrate the regulating circuit, it is represented in relation to a somewhat modified coating apparatus in FIG. 4. An amount of coating solution 01 equal to the amount which is to be coated on the high polymer web is fed through conduit 27 to the replenishing station 15, provided with a level regulating device which controls the supply of coating solution. Said device can be based on mechanical, hydraulical or electrical principles known per se and need no further explanation. At the outlet of the conduit 26 which is in connection with the collecting trough 17 an amount 02 of unused coating solution is added to Q1. The circulation circuit of the coating apparatus consists of a membrane pump 20 which pumps an amount 01 Q2 of said coating solution successively through a filter 21 and a flow-meter 22. The total amount of coating solution then flows through a temperature regulating device 23 whereupon it is forwarded to the distribution channels 11 which are situated adjacent to the coating pan 12. In this case the coating solution is fed into said channels through holes 19 placed at regular distances in a cover fixed on top of said channels. In the coating pan 12 an amount Q1 is picked up by the moving web. This amount is replaced by fresh solution which is added to the unused quantity Q2 ready for recycling to the coating pan. In order to regulate the flow in the coating pan the voltage-regulating device 24 controlling the speed of the membrane pump 20 is adjusted to the desired value.

The use of an external conduit has the supplementary advantage that no special precautions have to be taken relative to the thermostabilization of the coating pan. In prior art devices one had to provide the coating pan with double wall chambers through which adequate fluid flowed so that a considerable amount of energy was necessary to maintain the coating solution at the desired temperature. Moreover, the uniformity of the temperature throughout the coating pan depended on rather empirical methods and an exact control of the latter required complicated or very expensive apparatus.

It will be apparent to the skilled worker that the real form and dimensions of the displaceable end dams may pose a problem in this kind of coating apparatus. For the sake of clarity a rectangular section of a dam and the forces acting upon it is considered in FIG. 5a. The motion of the web 1 and the flow of the coating solution in a sense indicated by the arrow 30 gives rise to the formation of forces represented by their respective vectors 31 at the top and 33 at the inner side of the dam I4. Arrows 34 and 32 represent liquid flow beneath and above the dam. The force 31 results in the formation of a meniscus 36 as represented in FIG. 5c, whereas the force 33 causes a friction of the coating solution with the dam on the inner side thereof. The flows 32 and 34 are created by a difference of the level of the coating solution between the dams and at the outside thereof, and the flow 32 produces a supplementary meniscus 35 as can be seen in FIG. 5b. The meniscusses 35 and 36 tend to be irregular in shape and size. The side edge boundaries of the coating formed on the web are not well defined due to the instability of the meniscus 35, whereas due to the meniscus 36 the amount of coating solution applied to the zones of the web which travel immediately over and parallel with the dams is greater than the amount of coating solution applied to the portion of the web between the dams. The said adverse effects can be eliminated or at least reduced if the dams are specially shaped instead of having rectangular sectional profiles. the meniscus 35 may be reduced and stabilised by giving the dam a transverse cross-sectional shape as shown in FIG. 5d. The most important feature of the dam shaping is the chamfering of the outer top corner of the dam section. This chamfering creates a space which acts as a'kind of buffer which reduces the irregular flow of the liquid. The chamfering of the upper portion of the inside face of the dam is also valuable. For reasons of mechanical strength said dam is made relatively broad in the middle. lts upper and lower portions are tapered so as to assure-a continuous flow with minimum friction and a clearly defined space to build up a stable meniscus.

The meniscus 36 can be reduced and stabilised by shaping the front end portion of the dam so that it is somewhat tapered as represented in plan aspect in FIG. 5e.

The illustration of FIG. 6 represents a preferred embodiment of the mechanism which regulates the coating width. A support 40 fixed to the frame of the coating apparatus by adequate means is provided with a rod 41 which bears a screw 44 on its one extremity and a turning knob 45 on its other extremity. The screw 44 engages a sledge 43 engaging the guide plate 46. Said sledge 43 supports the displaceable end darn 14 by means of rivets 42. On turning the knob 45, the screw 44, engaging the sledge 43 causes the latter to slide on the guide plate 46. The displaceable end dam 14 being fixed to the sledge 43 slides simultaneously thus resulting in the regulation of the coating width.

It is clear that many variations of the foregoing coating apparatus may be applied by those skilled in the art. The device described is merely an example and the shape and spirit of the invention shall be derived from the appended claims.

We claim:

1. A coating apparatus for applying a liquid coating composition to a moving web, comprising arotatable backing roller for determining a path for the web, a coating pan disposed under said backing roller for holding coating solution in said web path, and means for continuously delivering coating solution into said pan, over the full length thereof, said coating pan having end dams which determine the effective internal length of the pan and which are shaped and located so that their top edges conform to the curvature of the surface of the backing roller but are spaced from that surface a distance substantially greater than the thickness of said web. at least one of said dams being displaceable for varying said effective length, and said coating pan also having an overflow edge over which liquid can continuously discharge fromthe pan over the whole of said effective length, which overflow edge is at a level above the level of the lowest points on the top edges of said dams.

2. A coating apparatus according to claim 1, wherein at least one of said end dams is provided with adjustment means, preferably screw adjustment means. which is accessible at an end of the coating pan and by which the position of the dam can be infinitely varied during operation of the apparatus.

3. A coating apparatus according to claim 1, wherein said coating solution delivery means includes a distributing channel which extends over the full length of the coating pan at the side opposite said overlfow edge, and from which liquid can continuously overflow into the coating pan.

4. A coating apparatus according to claim 3, wherein the inner faces of the upper portions of the end dams slope upwardly and outwardly towards the tops of-the said dams.

5. A coating apparatus according to claim 3, wherein the outer faces of the upper portions of the end dams slope upwardly and inwardly towards the tops of said dams.

6. A coating apparatus according to claim 1, comprising means for receiving coating solution which flows over said overflow edge and for receiving coating solution which discharges from the ends of said coating pan.

7. A coating apparatus according to claim 6, wherein the overflow edge is formed by a longitudinal wall portion of the coating pan.

8. A coating apparatus according to claim 1, wherein there is a gap between the end dams and the bottom of the coating pan to permit continuous discharge of liq uid from the pan, beneath such dams.

9. A coating apparatus according to claim 8, wherein the gaps between the end dams and the bottom of the coating pan are such that in operation of the apparatus the quantity of liquid discharging through such gaps in a given period of time is at least 25 of the amount of liquid which flows over said overflow edge in the same period of time.

10. A coating apparatus according to claim 1, wherein there are collecting spaces for collecting liquid which discharges from the ends of the coating pan, and a collecting space for collecting liquid flowing over the overflow edge, such collecting spaces being connected into a common recycling system.

11. A coating apparatus according to claim 10, wherein said collecting spaces are parts ofa single tray or other receptacle.

12. A coating apparatus according to claim 11, wherein said receptacle is connected with a vessel wherein a constant level of coating composition is maintained.

13. A coating apparatus according to claim 11, wherein said receptacle is provided with an outlet opening through which coating composition is pumped to a liquid supply opening or to liquid supply openings leading into said distributor.

14. A coating apparatus according to claim 1, wherein the coating pan is a shallow pan the bottom of which is adjacent the backing roller. 

1. A coating apparatus for applying a liquid coating composition to a moving web, comprising a rotatable backing roller for determining a path for the web, a coating pan disposed under said backing roller for holding coating solution in said web path, and means for continuously delivering coating solution into said pan, over the full length thereof, said coating pan having end dams which determine the effective internal length of the pan and which are shaped and located so that their top edges conform to the curvature of the surface of the backing roller but are spaced from that surface a distance substantially greater than the thickness of said web, at least one of said dams being displaceable for varying said effective length, and said coating pan also having an overflow edge over which liquid can continuously discharge from the pan over the whole of said effective length, which overflow edge is at a level above the level of the lowest points on the top edges of said dams.
 2. A coating apparatus according to claim 1, wherein at least one of said end dams is provided with adjustment means, preferably screw adjustment means, which is accessible at an end of the coating pan and by which the position of the dam can be infinitely varied during operation of the apparatus.
 3. A coating apparatus according to claim 1, wherein said coating solution delivery means includes a distributing channel which extends over the full length of the coating pan at the side opposite said overlfow edge, and from which liquid can continuously overflow into the coating pan.
 4. A coating apparatus according to claim 3, wherein the inner faces of the upper portions of the end dams slope upwardly and outwardly towards the tops of the said dams.
 5. A coating apparatus according to claim 3, wherein the outer faces of the upper portions of the end dams slope upwardly and inwardly towards the tops of said dams.
 6. A coating apparatus according to claim 1, comprising means for receiving coating solution which flows over said overflow edge and for receiving coating solution which discharges from the ends of said coating pan.
 7. A coating apparatus according to claim 6, wherein the overflow edge is formed by a longitudinal wall portion of the coating pan.
 8. A coating apparatus according to claim 1, wherein there is a gap between the end dams and the bottom of the coating pan to permit continuous discharge of liquid from the pan, beneath such dams.
 9. A coating apparatus according to claim 8, wherein the gaps between the end dams and the bottom of the coating pan are such that in operation of the apparatus the quantity of liquid discharging through such gaps in a given period of time is at least 25 % of the amount of liquid which flows over said overflow edge in the same period of time.
 10. A coating apparatus according to claim 1, wherein there are collecting spaces for collecting liquid which discharges from the ends of the coating pan, and a collecting space for collecting liquid flowing over the overflow edge, such collecting spaces being connected into a common recycling system.
 11. A coating apparatus according to claim 10, wherein said collecting spaces are parts of a single tray or other receptacle.
 12. A coating apparatus according to claim 11, wherein said receptacle is connected with A vessel wherein a constant level of coating composition is maintained.
 13. A coating apparatus according to claim 11, wherein said receptacle is provided with an outlet opening through which coating composition is pumped to a liquid supply opening or to liquid supply openings leading into said distributor.
 14. A coating apparatus according to claim 1, wherein the coating pan is a shallow pan the bottom of which is adjacent the backing roller. 